The present invention relates to an espresso machine or a fully automatic coffee machine having a grinder and an infusion device comprising an infuser and an infusion chamber.
The grain size distribution in a quantity of ground coffee powder or of ground coffee beans has a decisive influence on the infusion time of the coffee, the appearance and the taste of the finished coffee drink (for example espresso, café crème). This can be attributed to the fact that the grain size distribution determines inter alia the resistance of the ground coffee which the ground coffee offers to the water when water flows through the ground coffee, and hence the infusion time of the coffee.
Within the scope of the present invention, there is understood by grain size distribution, the frequency distribution of the average particle diameter of a defined quantity of ground coffee beans. In the case of a prescribed grinding disc spacing of the grinder, this grain size distribution typically has, both in the upper range of the grain sizes (coarse proportion) and in the lower range of the grain sizes (fine proportion), a local maximum in the frequency distribution: the grain size distribution can be characterised by the so-called x63.2 value. This value is defined such that 63.2% of the grains of a given grain size distribution have a smaller size than the x63.2 value. The x63.2 value can also be termed degree of grinding (also a different size value characterising the grain size distribution being able to be used as degree of grinding).
These two variables (grain size distribution and degree of grinding) are also used synonymously subsequently for simplification.
To date, the grain size distribution and/or the degree of grinding which an espresso machine or a fully automatic coffee machine delivers (such a machine is subsequently termed alternatively also fully automatic coffee machine or in brief coffee machine) has only been able to be assessed optically approximately or determined indirectly via the infusion time. However the latter also depends upon the metered quantity and the pressing force of the ground coffee in the infuser of the coffee machine. Adjustment of the grinder (subsequently also termed mill for simplification) of the coffee machine during production of the same has to date been effected merely via the grinding disc spacing, i.e. the spacing of the individual grinding discs of the grinder.
However, the grain size distribution only correlates partially with the spacing of the grinding discs and is subject to further non-adjustable variables, such as the plane-parallelism or the fine tooth depth of the respective pair of grinding discs. Adjustment of the grain size distribution via the grinding disc spacing cannot hence be ensured unequivocally and reproducibly. Very different degrees of grinding in the output of the coffee machine result therefrom despite the same adjustment of the degree of grinding. Furthermore, further factors, such as for example the type of beans or the degree of roasting, influence the grain size distribution, however these further factors are known in part only to the end customer. The degree of grinding is therefore adjusted only for the end customer of the coffee machine at the moment according to feeling (according to the taste of the coffee, according to the optical assessment of ground coffee grounds and/or according to the infusion time) by a customer services technician of the manufacturer of the coffee machine. Upon changing the type of beans or wear and tear of the grinding discs, renewed adjustment of the degree of grinding is hence required.